A thermally and/or thermo-mechanically highly stressed combustion space such as, for instance, a furnace, a hot gas duct or a combustion chamber in a gas turbine in which space a hot medium is produced and/or ducted is provided with a suitable lining as a protection against excessive thermal stressing. Said lining consists usually of a heat-resistant material and protects a wall of the combustion space from direct contact with the hot medium and the heavy thermal stressing associated therewith.
U.S. Pat. No. 4,840,131 relates to the securing of ceramic lining elements to a wall of a furnace or kiln, with a system of rails being secured to said wall. The lining elements are rectangular in shape with a planar surface and consist of a heat-insulating, fireproof, ceramic fibrous material.
U.S. Pat. No. 4,835,831 relates likewise to the affixing of a fireproof lining to a furnace wall, in particular a vertically arranged wall. A layer consisting of glass, ceramic, or mineral fibers is affixed to the metallic wall of the furnace. Said layer is secured to the wall by means of metallic hook members or by adhesive means. Wire netting having . . . —shaped meshing is affixed to said layer. The meshed netting serves also to prevent the ceramic-fiber layer from dropping. An even, closed surface of fireproof material is additionally applied secured by means of a bolt. The rebounding of fireproof particles formed during spraying, as would occur were the fireproof particles sprayed onto the metallic wall directly, will substantially be avoided as a result of applying the method described.
A ceramic lining of the walls of thermally highly stressed combustion spaces, for example of gas turbine combustion chambers, is described in EP 0 724 116 A2. The lining consists of wall elements made of high-temperature resistant structural ceramic material such as, for example, silicon carbide (SeC) or silicon nitrite (Si3N4). The wall elements are fastened mechanically and resiliently to a metallic supporting structure (wall) of the combustion chamber by means of a central fastening bolt. A thick thermal insulating layer is provided between the wall element and the wall of the combustion space so that the wall element is correspondingly distanced from the wall of the combustion chamber. The insulating layer, which is about three times as thick as the wall element, consists of ceramic fibrous material prefabricated in blocks. The wall elements can be accommodated in terms of their dimensions and external shape to the geometry of the space requiring to be lined. Another kind of lining for a thermally highly stressed combustion space is described in EP 0 419 787 B1. The lining consists of heat shield elements secured mechanically to a metallic wall of the combustion space. The heat shield elements are in direct contact with the metallic wall. To avoid excessive heating of the wall resulting from, for instance, a direct transfer of heat from the heat shield element or the ingress of hot medium into the gaps formed by the mutually abutting heat shield elements, the space formed by the wall of the combustion space and the heat shield element is exposed to cooling air, termed barrier air. Said barrier air prevents hot medium from penetrating as far as the wall and simultaneously cools the wall and the heat shield element.
WO 99/47874 relates to a wall segment for a combustion chamber and to a combustion chamber of a gas turbine. Described therein is a wall segment for a combustion chamber, which can be impinged upon by a hot fluid, for example a hot gas, having a metal support structure and a heat protection element secured thereon. Fitted between said metal support structure and said heat protection element is a deformable separating layer whose purpose is to absorb and compensate for possible relative movements of the heat shield element and support structure. Such relative movements can be caused, for example, in the combustion chamber of a gas turbine, in particular an annular combustion chamber, by the materials used having different thermal expansion characteristics or by pulsations in the combustion area that can occur in the event of irregular combustion to produce the hot working medium or as a result of resonant effects. At the same time the separating layer results in the relatively inelastic heat protection element overall lying flatter on the separating layer and metallic support structure because the heat protection element penetrates in places into the separating layer. The separating layer can thus also compensate for irregularities, due to production effects, on the support structure and/or heat protection element, which can lead to the disadvantageous introduction of forces at specific points, locally.
Particularly in the case of walls of high-temperature gas reactors such as, for example, gas turbine combustion chambers operated under pressure, their supporting structures have to be protected by means of suitable combustion chamber linings against an attack by hot gas. Owing to their high temperature stability, corrosion resistance, and low thermal conductivity, ceramic materials are ideal candidates for this compared to metallic materials. Owing to thermal expansion properties that are typical of materials and cause movement in the presence of differences in temperature (ambient temperature when stopped, maximum temperature when fully loaded) typically occurring during operation, the thermal mobility of ceramic heat shields resulting from temperature-dependent expansion has to be accommodated to obviate the occurrence of thermal stress which obstructing expansion causes and can lead to component destruction. This can be achieved by lining the wall requiring to be protected from hot gas attack with a plurality of individual, size-limited ceramic heat shields, for example heat shield blocks made of fireproof ceramic: As already discussed above in connection with EP 0 419 487 B1, suitable expansion gaps which, as explained, must for safety reasons never be completely closed even in the hot condition must be provided between the individual ceramic heat shield elements. It must at the same time be ensured that the hot gas does not excessively heat the supporting wall structure via the expansion gap. The simplest and surest way to avoid this in a gas turbine combustion chamber is to flush the expansion gap with air, by a process termed barrier-air cooling. The air required in any event for cooling mounting elements for the ceramic heat shields can be used for that purpose.
WO 02/25173 A1 discloses a heat shield brick, in particular for lining a combustion chamber wall, comprising a hot side that can be exposed to a hot medium, a wall side that lies opposite the hot side, and a peripheral side that lies adjacent to the hot side and the wall side and that has a peripheral lateral face. A tensioning element, pre-stressed in the peripheral direction, is provided on the peripheral side, whereby a compressive stress is generated perpendicularly to the peripheral lateral face. Extremely efficient and long-lasting protection for a heat shield brick is indicated thereby. The tensioning element is pre-stressed in the peripheral direction, whereby a certain compressive stress is generated perpendicularly to the peripheral lateral face. The heat shield brick is secured by this normal force, which is directed toward the interior of the heat shield brick at its center, even when the normal forces are very small. An incipient crack in the material, resulting from, for instance, impact loading, will be effectively counteracted thereby. Given a suitably arranged and embodied tensioning element, any incipient cracks present in the material will not, or only to a limited extent, be able to develop further or expand. The tensioning element holds the heat shield brick together, as it were, and protects it on the one hand from incipient cracking and, on the other, primarily from cracking through completely. The danger of smaller or larger fragments becoming loose or dropping out in the possible event of complete cracking through is additionally effectively counteracted.